The overall objective of this project is to understand the molecular basis of two types of monoamine oxidase (MAO A and B) at the gene level. MAO is an important enzyme in catecholamine metabolism. Abnormal levels of MAO activity have been shown in a number of mental disorders. With the full-length human liver MAO A and B cDNAs cloned in this laboratory, the genomic organizations and the expressions of these genes will be investigated. These studies have great importance for both basic and clinical research. The specific aims of this five-year grant application are described below. Using the established bacterial and mammalian cell expression plasmid vectors, the cloned human liver MAO A and B cDNAs will be expressed and the catalytic properties of the expressed proteins will be characterized. Using Northern blot analysis with MAO A and B cDNA as probes, the correlation among the expressions of these genes at the levels of mRNA, protein and catalytic activities in various human tissues will be examined. This study will indicate whether the tissue specificity of MAO A and B is controlled at the level of transcription or translation. Using Southern blot analysis of cells containing human chromosomes - mouse DNA hybrid as well as in situ hybridization, the chromosomal location of human liver MAO A and B genes will be determined. This fundamental knowledge is essential for studying the role of MAO genes in mental disorders. The genomic DNAs for MAO A and B will be analyzed. Several human genomic libraries (cosmid and lambda) will be screened using MAO A and B cDNA probes, the genomic DNAs encoding human liver MAO A and B genes will be cloned. The restriction maps of the genomic MAO A and B clones will then be constructed. Further, the MAO A and B genes will be sequenced by the chain termination method, and their promoter regions will be analyzed. The heterogeneity of MAO A and B will be investigated. Using the similar procedures used to clone human liver MAO cDNA clones, MAO A, B and related cDNAs will be cloned from other human tissues, and their DNA and amino acid sequences will be compared. Thus, the similarities and differences of MAO A (or B) from various tissues will be clearly understood. This information will provide a conclusive answer on the validity of using platelet MAO B as a marker for brain MAO B and will have significant implications on future clinical studies.